Laser flow cells are designed and constructed to enable laser light to more accurately propagate through a liquid media, typically containing dissolved particles. The liquid media presents one or more chemical species to interact with the laser light. The material in the liquid media may be used for light scattering in conjunction with a light scattering read head. The degree of scattering can help to characterize the material carried by the liquid with regard to its molecular weight and the size of its molecules. Typical liquids used are those in which dissolution of the material can be accomplished, and include water and toluene to name but two.
The sample cell configuration includes a flow cell mounted within a support. The flow cell has a bore to carry the fluid, and is surrounded by an array of scattering detectors. The fluid sample is introduced into the bore and is longitudinally illuminated within the bore by a collimated beam of light such as from a HeNe laser or semiconductor laser.
The structures through which the light beam propagates on its way into and out of the bore are matched as nearly as possible to mitigate the effect of any difference in refractive index in the materials. Positional accuracy, precision and reproduciblity is of paramount importance.
Previous flow cells have lacked the accurate and reproducible alignment which is desired in flow cell construction. Aspects of a flow cell tending to degrade its performance include non-alignment of the cell retainers with respect to the cell, of which two are typically used, both with respect to the laser beam and with respect to each other. For example, flow cells which have only seals separating the cell from the cell manifolds will have an alignment dependent upon the skill of the cell assembler.
In some flow cells, the stray light cover was used as an alignment device. The removal of the stray light cover would immediately subject the flow cell to mis-alignment. In other flow cells, the horizontal alignment depends upon the mating of vertical manifold surfaces with vertical read head surfaces. The tolerances on this fit can not normally be held due to any misalignments occurring in the cell assembly, thus destroying horizontal alignment.